Phonograph pickup cartridge for four channel recordings

ABSTRACT

A magnetic phonograph pickup, especially adapted for four channel sound reproduction is disclosed wherein the four channel output is produced by an elongated tubular armature of permeable material pivotally mounted at one end for movement of its opposite end within a quadrangular cluster of four pole pieces. The four pole pieces form the terminal portions of two closedpath magnetic circuits, each completed through a pair of cores with voltage generating coils mounted thereon. Straps of highly permeable material magnetically couple the cores of each circuit and the straps are separated from one another by a nonmagnetic, electrically conductive shield which acts as an eddy current shield to any stray external fields. Magnetomotive force is provided by a stationary permanent magnet magnetically coupled with the pivotally mounted end of the moving armature to minimize motion between the permanent magnet and armature in the region of the magnetic coupling.

Stanton [451 Nov. s, 1974 PHONOGRAPH PICKUP CARTRIDGE FOR FOUR CHANNEL RECORDINGS [76] Inventor: Walter O. Stanton, Laurel Hill Rd.,

Laurel Hollow, NY. 11948 [22] Filed: Mar. 29, 1973 [211 Appl. No.: 346,008

52 us. c|.... 179/100.41 K, 274/37 [51] Int. Cl ..H04r11/12 [581' Field of Search l79/l00.4l K, 100.41 S, 179/].41 Z, 100.4 T, ,1 OD; 274/37 [56] References Cited- UNITED STATES PATENTS 3,546,399 12/1970 Stanton et al.... 179/100.4l K 3,641,284 2/1972 Westerkamp.... l79/l00.4l K 3,700,829 10/1972 Anneberg l79/l00.41 K 3,720,796 3/1973 Honma l 179/100.41 K 3,760,125 9/1973 Lave 274/37 Primary Examiner-Alfred H. Eddleman Attorney, Agent, or Firml(ane, Dalsimer, Kane,

Sullivan and Kurucz [5 7] ABSTRACT A magnetic phonograph pickup, especially adapted for four channel sound reproduction is disclosed wherein the four channel output is produced by an elongated tubular armature of permeable material pivotally mounted at one end for movement of its opposite end within a quadrangular cluster of four pole pieces. The four pole pieces form the terminal portions of two closed-path magnetic circuits, each completed through a pair of cores with voltage generating coils mounted thereon. Straps of highly permeable material magnetically couple the cores of each circuit and the straps are separated from one another by a nonmagnetic, electrically conductive shield which acts as an eddy current shield to any stray external fields. Magnetomotive force is provided by a stationary permanent magnet magnetically coupled with the pivotally mounted end of the moving armature to minimize motion between the permanent magnet and armature in the region of the magnetic coupling.

8 Claims, 6 Drawing Figures PAIENTEIJnnv 5 1914 31846592 saw u: 5

PATENTEDNDV 51914 3.846 592 SHEET Hf 5 m wt NQV

PHONOGRAPH PICKUP CARTRIDGE FOR FOUR CHANNEL RECORDINGS BACKGROUND OF THE INVENTION The present invention relates to a new and improved magnetic phonograph pickup of the moving iron type and in particular to a pickup adapted for use with discrete four channel records as well as conventional stereophonic and monaural record discs.

Quality stereophonic phonograph pickups are designed to maintain effective separation on the order of 20-30 dbs between the two output channels throughout the audio spectrum, which for most practical purposes ranges between l20 HZ and 20,000 HZ. Beyond the upper audio frequency limit, the separation between the channels falls off sharply and, in some cases, the cross-talk signal between channels may exceed the direct output signal for the channel. Heretofore, this phenomena has been regarded as immaterial since it occurs at frequencies higher than 20,000 HZ and thus does not affect the output of the stereophonic speakers.

Recently, quadraphonic or four discrete channel record discs and audio systems have been introduced and are gaining in popularity. The four channels are obtained from the record disc by providing each of the conventional stereophonic channels with a second channel consisting of a 30,000 HZ frequency modulated carrier. The conventional or AM channel signals are fed through a first stereo amplifier to drive a first dulations of a stylus in the groove of a record when the set of speakers while the frequency modulated signals are demodulated and then fed through a second stereo amplifier to drive a second set of speakers.

Since the third and fourth channels of quadraphonic systems are derived from a 30,000 HZ carrier, it should be apparent that a cartridge suitable for use in a quadraphonic system must maintain suitable channel separation through both the AM band as well as the FM band of the four channel record discs. This requires a cartridge able to provide acceptable channel separation and fidelity of reproduction through a frequency range of approximately 15 and 50,000 HZ.

In view of the above, it is the principal object of the present invention toprovide an improved phonograph pickup having a generally flat frequency response and capable of maintaining channel separation throughout the audio frequency spectrum and modulated frequency spectrum of discrete four channel record discs.

SUMMARY OF THE INVENTION The above and other beneficial objects and advantages are attained in accordance with the present invention by providing a magnetic phonograph pickup of the replaceable stylus type which comprises a supporting structure forming a cartridge body. Two magnetic circuits formed of highly permeable material are supported within the body. Each of the circuits includes first and second core means terminating respectively in first and second pole pieces in opposed spaced relationship. The pole pieces of the first circuit being interdigitated with those of the second circuit to form a quadrangular cluster about a common space. A strap of highly permeable material forms a low reluctance path magnetically coupling the pole pieces. of the first magnetic circuit and a second strap of highly permeable system is in operative position.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. I is a perspective view of a magnetic pickup embodying the present invention;

FIG. 2 is an exploded view showing the several parts making up the cartridge body of the pickup illustrated in FIG. I; I

FIG. 3 is a longitudinal sectional view of the molded plastic body parts of the present pickup with the parts assembled thereon;

FIG. 4 is a cross-sectional view taken along reference lines 4-4 of FIG. 3 in the direction indicated by the arrows;

FIG. 5 is a cross-sectional view taken along reference lines 5-5 of FIG. 3 in the direction indicated by the arrows; and,

FIG. 6 is a sectional view taken along reference lines 6-6 of FIG. 3 in the direction indicated by the arrows.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Reference is now made to the associated drawings wherein the present cartridge is illustrated and wherein similar components bear the same reference numerals 'throughout the several figures. Reference is firstmade I2 is generally described in the above referenced, commonly assigned patent although it should be realized that variations in the configuration of the stylus tip, per se, may be necessary to enable it to adequately track both the AM and FM signals of the four channel record groove.

The cartridge body includes a transducer system which will be described in more detail forthwith which responds electrically and magnetically to the motion of the moving system to produce a four channel output which is fed out through terminal pins 16, 18, 20 and 22 to the associated preamplifiers and amplifiers of the four'channelsystem. The transducer system is contained within a container 24 formed of a highly permeable material and serves to enshroud the transducers and shield them from stray signals. A bracket 26 secured to the top of the container provides means for securing the cartridge to a phonograph player tone arm.

Turning more particularly to the cartridge body and transducer system mounted therein, the present inventwo molded plastic parts, 28 and 30, each provided with integral interlocks, such as that illustrated at 32, designed to permit the body parts to be snap fitted together to form a tight assembly. In this connection, the

first molded body part 28 includes a platform 33 provided with holes 34 and 36 through which left and right channel core means 38 and 40 extend from below. The core means formed of highly permeable material terminate in left and right channel pole pieces 42 and 44 respectively. Platform 33 also includes holes 46 and 48 through which a second set of left and right channel core means 50 and 52 extend from below. Core means 50 and 52 which are also formed of highly permeable material terminate respectively in pole pieces 54 and 56.

Voltage generating coil bobbins 58 and 60 upon which are wound voltage generating coils 66 and 68 are In this regard, it is to be noted that bobbin 58 is'provided with a generally rectangular opening 110 which, in addition to receiving the stem portion of core 38, is also sufficiently large to receive leg 84 of strap 78. The opening 110 is such as to maintain leg 84 and the stem of core 38in a closely abutting relationship as shown in FIG. 4. In a similar manner (as also shown in FIG.

4), the stem of core 40 is maintained in a closely abutplaced over the portion of core means 38 and 40 extending above platform 33. Similarly, voltage generating coil bobbins 62 and 64 upon which are wound voltage generating coils 70 and 72 are placed respectively over the portions of core means 50 and 52 extending above platform 33. In this regard, a thin nonmagnetic card or sheet 74 with suitable eyelets 76 to receive the stems of core means 38, 40, 50 and 52 helps secure the cores and coils in position during assembly.

A first strap of highly permeable material 78 cornpletes the left channel magnetic circuit assembly in a manner to be described forthwith and similarly, a second strap 80 formed of the same material completes the second magnetic circuit assembly. In this regard, strap 78 comprises a flat, generally Z-shaped base 82 from which legs 84 and 86 depend. Similarly, strap 80 comprises a generally backward Z-shaped base 88 from which legs 90 and 92 depend.

The cartridge further includes a resilient metal strap 94 which serves the double purpose of grounding the interior metal parts of the cartridge to the inner surface of container 24 and serving as an eddy current shield in the manner to be described forthwith. For the present, it suffices to say that strap 94 is formed of an electrically conductive, nonmagnetic resilient material such as copper. Strap 94 is bent over itself to define a bottom and top part 96 and 98 respectively. The planar configuration of bottom part 96 is such as to permit it to pass through opposed legs84 and 86 of core strap 78 and 90 and 92 of core strap 80. It should also be noted that an internal portion 100 of top part 98 is integrally hinged and extends downward from the top part forming a resilient tongue.

A final element in the cartridge construction is permanent magnet 102 which is cemented in position within a recess 104 positioned at the front end of molded part 30. Magnet 102 includes a semi-circular indentation 106 at its base which is-aligned with an opening 108 that extends through body part 30 thereby providing access for the moving system armature to the space between the pole pieces in the assembled cartridge. Y

The assembly of the present cartridge is best illustrated with regard to FIGS. 3, 4 and 5. As previously mentioned, core 38'passes upwardly through opening 34 in platform 33 to receive the bobbin 58 of coil 66.

ting relationship with leg 90 of core strap 80 by opening 112 in bobbin of coil 68. Referring now to FIG. 5, it can be noted that the stem of core means 52 is held in a closely abutting relationship with leg 92 of strap by the portions of bobbin 64 defining opening 114. Similarly, the stem of core means 50 is held in closely abutting relationship with leg 86 of core strap 78 by the opening 116 defined in bobbin 62.

As best seen in FIG. 5, pole pieces 42, 44, 54 and 56 form a quadrangular cluster with the two left channel pole pieces 42 and 54 in opposed relationship and interdigitated with the two right channel pole pieces 54 and 56 which are also in opposed relationship. The two left channel pole pieces thus form the terminals for a first magnetic circuit which comprises pole piece 42, the stem of core 38, core strap leg 84, core strap base 82, core strap leg 86, the stem of core 50, and then terminates in the other pole piece 54. Similarly, the other magnetic circuit comprises pole piece 44, the stern of core 40, core strap leg 90, core strap base 88, core strap leg 92, the stem of core 52 and then terminates in pole pieces 56. As stated, the elements of both magnetic circuits are formed of a highly permeable material, such as an alloy of iron and nickel, or of iron, nickel and aluminum as, for instance, Hy-mu 80.

As can also be seen in FIG. 4 and 5, the bottom part 96 of ground strap 94 separates the bases 82 and 84 of core straps 78 thereby serving as an eddy current shield while the top part 98 of strap 94 engages the inner part of shell 24 thereby grounding the coils to the shell. In

this connection, it should be noted that the depending portion of strap 94 engages the top surface of base 82. The resiliency of strap 94 ensures a firm connection between the various parts.

Flux for the magnetic circuits is provided by a moving system 12, which, as previously mentioned, is described in detail in U.S. Pat. No. 3,546,399. Suffices to say, the moving system 12 as shown in FIG. 3 comprises a tubular casing 118 of nonmagnetic material such as aluminum or copper carried by plastic housing 120 which mates with the front of container 24, as shown in FIG. 1. A moving iron armature 122 is longitudinally mounted within casing ll8'and connected to stylus 14 by tube 124 formed of a light, nonmagnetic material.

In this regard, a suitable spacer and damping device such as collar 126 made of a rubber, synthetic rubber or other flexible material is disposed about the forward end of armature 122 and engages the inner surface of tubular casing 118, so that the entire moving assembly including-the stylus, stylus tube and moving iron armature can oscillate in response to the stylus following modulations of the walls of the record groove. It should be noted that ring 126 is adjacent the lower end of magnet 102 so that the relative position of the armature and magnet remains constant and the degree of magnetization of the armature does not vary with movement of the armaturesince there is no relative movement be- .tween the armature and magnet at the point of magmagnet. The moving system is completed by a tie-wire 128 of a nonmagnetic spring metal extending between the lower rear portion of the'tubular casing 118 to the forward end of armature 122.

The first magnetic circuit defines a flux path for the left output channels and the second magnetic circuit defines a flux path for the right output channels of the cartridge. It is to be noted that the eddy current shield defined by the portion 96 of strap 94 separates the two magnetic circuits. It has been found that the eddy current shield provides additional high frequency separation between the right and left channels. Without the eddy current shield and the separate core straps, unacceptably high levels of crosstalk have been encountered.

The cartridge construction is completed by tying together the two right channel coils and two left channel coils and connecting them to the appropriate terminal pins extending from the bulkhead at the rear of part 28.

Card 74 provides a convenient terminal block for making the necessary connections; Accordingly, the start 130 of left channel coil 70 is connected to the start 132 of left channel coil 66 through contact 134 of card 74. The finish 135 of coil 66 is connected to pin 16 andthe finish 138 of coil 70 is connected to pin 20. Similarly, the start 142 of coil 68 is connected to the start 144 of coil 72 through contact 146 and the finish 148 of coil 72 is connected to pin 18 while the finish 152 of coil 68 is connected to pin 22. Pins and 22 are then grounded through strap 156 which engages shell 24. As previously stated, the magnetic circuits are also grounded to the shell through strap 94. In this connection, the hinged portion 100 of strap 94 insures a firm contact with the core strap 78 and 80 as shown in FIG. 3. Pin 136 thus carries the left channel signals and pin 150, the right channel signals.

ln operation, the stylus tip 14 of the moving system tracks the groove on.a record disc and in so doing, causes the magnetized armature 122 to move within the pole piece cluster in response to the record groove track. As stated, the pole pieces associated with each channel are positioned opposite each other so that motion of the stylus in response to the right channel signal will cause the armature to move along a path having components toward and away from polepieces 44 and 56. This produces a change in the flux in the right channel core means 40 and 52. thereby inducinga voltage in the associated coils 68 and 72 which appears as the signal at terminal 18. In a similar manner, motion of the stylus in response to the left channel signalwill cause the armature to move along a path having components toward and away from pole pieces 42 and 54. This produces a change in the flux in the left channel core means 38 and 50 thereby inducing a voltage in its associated coils which appears as the signal at terminal 16.

. noted that the eddy current shield provided by strap 94 and the separation of the right and left core straps are essential to maintaining good separation of the two high frequency signals.

Having thus described my invention, what I claim is:

6 1. A magnetic phonograph pickup suitable for use in reproducing four channel recordings comprising:

a pair of separated magnetic circuits, each terminating in a pair of pole pieces with the pole pieces ar- 5 ranged in a quadrangular cluster;

a moving system with a stylus and a supporting magnetic armature mounted for pivotal movement between the cluster of pole pieces; and,

a nonmagnetic, electrically conductive, eddy current shield interposed between and in electrical contact with portions of said magnetic circuits intermediate said pole pieces.

2. A magnetic phonograph pickup of the replaceable stylus type for use in reproducing four channel recordings comprising:

a supporting structure forming a cartridge body; two magnetic circuits formed of permeable material supported within said body, each magnetic circuit including first and second core means, said core means terminating respectively at one end in first and second pole pieces in opposed spaced relationship, the four pole pieces from said two magnetic circuits being interdigitated to form a quadrangular cluster about a common space and a separate strap for each circuit magnetically coupling the other ends of the first and second core means of each circuit;

a nonmagnetic, electrically conductive, eddy current shield interposed between and separating the straps of the two magnetic circuits;

voltage generating means including a coil mounted on at least one of said cores of each of said magnetic circuits; and,

a moving system removably coupled to said cartridge body including a record engaging stylus, a tubular armature of magnetic material extending into said body from one end thereof when said system is in operative position, stylus connecting means pivotally mounting said armature at one end, said armature one end being outside the common space between the pole pieces for movement of the opposite end of the armature within the common space formed by the quadrangular cluster of pole pieces in response to the undulations of the stylus in a record groove when the system is in operative position.

3. The magnetic phonograph pickup of claim 2 wherein said tubular armature is formed of a permeable material and further comprising:

a flux source including a stationary, permanent magnet mounted-on said supporting structure proximal said cartridge one end immediately adjacent said armatureone end and magnetically coupled at one of its poles to the pivotally mounted end of the armature, whereby the relative motion between the permanent magnet and armature in the region of magnetic coupling is minimized and the armature is maintained in a substantially uniform and constant state of magnetic saturation.

4. The magnetic phonograph pickup of claim 2 further comprising four voltage generating coils, one mounted on each of said core means.

5. The magnetic phonograph pickup of claim 4 wherein the coils of each of the magnetic circuits are interconnected.

whereby said two magnetic circuits are grounded to said shield.

8. The invention in accordance with claim 2 wherein each of said coupling straps includes a base portion and legs depending therefrom, each of said .legs being adapted to abut against one of the core means of the associated magnetic circuit and said eddy current shield is interposed between the bases of the core straps. Y 

1. A magnetic phonograph pickup suitable for use in reproducing four channel recordings comprising: a pair of separated magnetic circuits, each terminating in a pair of pole pieces with the pole pieces arranged in a quadrangular cluster; a moving system with a stylus and a supporting magnetic armature mounted for pivotal movement between the cluster of pole pieces; and, a nonmagnetic, electrically conductive, eddy current shield interposed between and in electrical contact with portions of said magnetic circuits intermediate said pole pieces.
 2. A magnetic phonograph pickup of the replaceable stylus type for use in reproducing four channel recordings comprising: a supporting structure forming a cartridge body; two magnetic circuits formed of permeable material supported within said body, each magnetic circuit including first and second core means, said core means terminating respectively at one end in first and second pole pieces in opposed spaced relationship, the four pole pieces from said two magnetic circuits being interdigitated to form a quadrangular cluster about a common space and a separate strap for each circuit magnetically coupling the other ends of the first and second core means of each circuit; a nonmagnetic, electrically conductive, eddy current shield interposed between and separating the straps of the two magnetic circuits; voltage generating means including a coil mounted on at least one of said cores of each of said magnetic circuits; and, a moving system removably coupled to said cartridge body including a record engaging stylus, a tubular armature of magnetic material extending into said body from one end thereof when said system is in operative position, stylus connecting means pivotally mounting said armature at one end, said armature one end being outside the common space between the pole pieces for movement of the opposite end of the armature within the common space formed by the quadrangular cluster of pole pieces in response to the undulations of the stylus in a record groove when the system is in operative position.
 3. The magnetic phonograph pickup of claim 2 wherein said tubular armature is formed of a permeable material and further comprising: a flux source including a stationary, permanent magnet mounted on said supporting structure proximal said cartridge one end immediately adjacent said armature one end and magnetically coupled at one of its poles to the pivotally mounted end of the armature, whereby the relative motion between the permanent magnet and armature in the region of magnetic coupling is minimized and the armature is maintained in a substantially uniform and constant state of magnetic saturation.
 4. The magnetic phonograph pickup of claim 2 further comprising four voltage generating coils, one mounted on each of said core means.
 5. The magnetic phonograph pickup of claim 4 wherein the coils of each of the magnetic circuits are interconnected.
 6. The magnetic phonograph pickup in accordance with claim 2 further comprising a shield of magnetic material enshrouding said supporting structure.
 7. The magnetic phonograph pickup of claim 6 further comprising grounding means extending between said metallic shield and said eddy current shield whereby said two magnetic circuits are grounded to said shield.
 8. The invention in accordance with claim 2 wherein each of said coupling straps includes a base portion and legs depending therefrom, each of said legs being adapted to abut against one of the core means of the associated magnetic circuit and said eddy current shield is interposed between the bases of the core straps. 